1. Field of the Invention
The present invention relates to a control circuit for a motor wherein clutch to brake devices are electromagentically actuated to intermittently connect the motor and a load, thereby controlling the rotating speed of a shaft.
2. Description of the Prior Art
One system for controlling the shaft speed of a clutch motor having clutch and brake devices is disclosed in U.S. Pat. No. 3,599,764. In the shaft speed control system, the operation speed of the drive shaft of a utilization device is maintained at a preselected value by generating a rectified DC signal and a superimposed AC signal when it falls below a reference value, indicating a low shaft speed and causing energization of the clutch for increasing the shaft speed. When the shaft speed becomes greater than selected value, the generated signal exceeds the reference value and is detected by a second solid state switch causing action of the brake until the shaft speed decreases. Alternating pulse-like nonoverlapping actuation of the clutch and brake devices maintains the utilization device drive shaft at the selected speed. The control system, however, forms an AC signal of the shaft speed measuring means into the superimposed AC signal by a rectifier and an R-C element having a predetermined time constant, and therefore involves the disadvantage that the shaft speed cannot be precisely controlled over a wide range from low speeds to high speeds.